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A firefighting helicopter makes a drop on a slope in the foothills near Los Angeles on Sunday. ((Ric Francis/AP))

A wildfire forced 1,000 people from their homes in the foothills northeast of Los Angeles on Sunday, officials said.

More than 400 firefighters fought the 140-hectare fire, aided by two helicopters and water-dropping air tankers, said Elisa Weaver, a spokeswoman for Sierra Madre's Arcadia Fire Department. Residents were forced to leave at least 550 homes Saturday night and Sunday, but none had burned.

"This is pretty serious," Weaver said. "Some of these areas have not burned in over 40 years."

Smoke and fire billowed near neighbourhoods on the outskirts of Sierra Madre near Bailey Canyon Wilderness Park. The fire moved slowly as it fed on brush and was estimated to be five to 10 per cent contained. It is expected to continue burning for another two or three days.

Winds were calm early Sunday, boosting firefighter efforts, Weaver said.

Helicopters made water drops Sunday morning on a steep ridge above Sierra Madre, about 24 kilometres northeast of Los Angeles and just east of Pasadena. A fixed-wing water tanker also made at least one drop of flame retardant.

Wedding group left stranded

The fire also stranded 50 guests from a wedding party at the Chantry Flats ranger's station on Saturday until they were airlifted out Sunday afternoon, Weaver said. It took five helicopter trips from the ranger's station to the parking area where the wedding party's cars were parked. The party then was escorted out by road.

The fire was first reported Saturday afternoon in a wooded area a few kilometres northeast of Pasadena. It was windy at the time and unseasonably hot, with temperatures approaching 100 degrees.

The flames also caused the evacuation of a boy scout camp Saturday and left about 100 hikers stranded in a parking lot. Most of the scouts had already left the camp by the time the evacuation of the area was ordered, Weaver said, and no injuries were reported.

Firefighters originally had hoped to have the fire contained Sunday, but gusting winds late Saturday night kept the fire out of control and sent it creeping toward nearby homes. The mandatory home evacuations came shortly before 11 p.m. PT.

Two shelters have been set up for evacuees.

Flames outlined steep ridges about a kilometre above Sierra Madre, a San Gabriel Mountains foothill community of about 11,000 popular with artists.

To the south in San Diego County, about 16 hectares burned in thick brush about 24 kilometres north of downtown San Diego. No injuries or property damage had been reported, a San Diego Fire Department spokeswoman said.